The present invention relates to a bar-pusher actuation device for bar feeders applied to machine tools, in particular lathes equipped with a movable or fixed head.
In fixed-head lathes, after the front part of the bar has been inserted in the head and moved to the required point (usually for a facing operation), the lathe begins its working cycle: the chuck of the head opens and the bar must advance by a certain and precise length. The working cycle begins once the chuck is closed.
In normal feeders, the bar is pushed forward until it abuts an appropriate bar-stopper, and after this the thrust can continue until the new advancement occurs or can be discontinued during the working cycle and be restored at the end of the cycle.
This operation has several disadvantages:
a) a bar-stopper, which is an often complicated and bulky element, has to be mounted on the lathe; PA1 b) the bar, in advancing, collides against the bar-stopper and can rebound, causing variations in the lengths of the part.
If the operation is of a continuous push type, besides the already mentioned disadvantages, small-diameter bars flex and cause other disadvantages: vibrations, noise, wear of the bars.
As regards automatic lathes of the so-called movable-head type, it is possible to move the bar, to be machined, forward or backward.
The feeding of the bar into the head is caused by the bar-pusher of the feeder, which is actuated by a linear actuator which comprises a chain moved by a drive unit.
During the machining, the bar held by the head moves in both directions, in particular in the direction opposite to the advancement direction, so that a thrust against the bar-pusher is exerted and forces said bar-pusher to move backward. In particular when the bars have a small diameter, it often occurs that the pressure exerted by the head on the bar being machined causes its deformation or at least a nonrecoverable stress inside the guiding channel.